In 'Railway Archive' 35 there are photographs of 'Hercules' (page 48) and Boulton's Bury 0-4-0 No 26 (page 59) for which see pages 32 and 33 of 'The Chronicles of Boulton's Siding.
There is also an article, 'Notes on the Chronicles of Boulton's Siding' in the Locomotive Magazine for March 1931 , pages 92 & 93. This has a small photo of the Stephenson long-boiler 0-6-0 'Lord Robartes'.
More interesting perhaps is the drawing of Boulton's owner's plate.
(The 1931 article may have been incorporated in the David & Charles reprint, in which case apologies for cluttering this thread with stuff you already know! I haven't seen a copy of the reprint for donkey's years, and my copy of the Chronicles is one of the 1927 originals, a fortunate and much prized acquisition!)
I hoping this is of use.
Regards, David.